1. Field of the Invention
The invention relates to the technical field of an optical mouse and, more particularly, to a light brightness controller for an optical mouse.
2. Description of Related Art
Typically, an optical mouse uses a light emitted diode (LED) to illuminate a pad or other object and an image sensor to obtain image frames on the pad for comparing a previous and a current images and obtaining a motion vector of the optical mouse. FIG. 1 is a block diagram of the optical mouse, which includes a light source 210, a resistor 220 and an optical processor 230. The light source 210 is an LED to vary current flowing through the light source 210 by the resistor 220, thereby determining the brightness of the light source 210. There are two types where a frame signal indicates a start or synchronous signal of each image frame for controlling lighting of the LED, as shown in FIG. 2 illustrating a control timing diagram of lighting the LED. The first type is a normal mode, which the LED 210 lighting or not is determined by using the optical mouse or not, i.e., the LED 210 is lighted when the optical mouse is active and not lighted when the optical mouse is idle. Therefore, the lighting active/idle time covers the entire frame. The second type is a shutter mode, which the LED 210 lighting or not is determined by using a shutter or not (FIG. 2), i.e., the LED 210 is lighted only when the shutter is active. Further, the exposure amount received by the optical processor 230 is changed in accordance with on/off time of the shutter.
In the optical mouse, as the resistor 220 is soldered to a printed circuit board (PCB), the current flowing through the light source 210 is fixed without the flexibility to the brightness of the light source 210. If the optical processor 230 has high sensitivity to rays, the light source 210 is continuously lighting while the shutter is opened or even the optical mouse is active. Thus, it can be happened that the shutter cannot be shrunk but an image sensed by the optical processor 230 still presents in saturation, so that the optical mouse cannot have associated detection.
Further, the optical mouse facing surfaces with deeper colors needs longer shutter time to image, but the light source 210 has to keep on a certain high brightness due to processing speed requirement. In addition, the light source 210 requires longer lighting time at suspend (current standard limit for USB Suspend to 500 μA), so that the current standard limit cannot be met. Thus, the prior optical mouse cannot perform motion detection by a function of motion wakeup at suspend.
Further, the light source 210 lighted off can cause very high instant current consumption so as to cause noises. FIG. 3 illustrates current flowing through the light source 210. As shown in FIG. 3, due to imaging differences, when the light source 210 is turned on or off (respectively indicated by A and B in FIG. 3), appearance of the respective over-shooting and under-shooting can easily cause mistakes to the optical mouse, where a frame signal indicates a start or synchronous signal of each image frame.
Therefore, it is desirable to provide an improved light brightness controller for an optical mouse to mitigate and/or obviate the aforementioned problems.